Coiled springs have long been used to provide self closing mechanisms for various light weight household doors such as fly wire doors, hinged gates etc. A coiled spring is connected between the gate post and a point on the gate away from the hinged edge so that on opening the gate the spring stretches around the hinged edge, thereby providing a biasing force which acts to close the gate. This type of self closing mechanism is not readily adaptable to sliding doors since the spring is required to stretch the full distance moved by the door. This may cause over extension and deformation of the spring and can result in an excessive closing force being applied to the door in the fully opened position.
Pneumatic cylinder/piston devices are normally used to provide self closing mechanisms for heavier doors. These cylinder/piston devices can be expensive to produce and suffer from the disadvantage that the biasing force is dependent on the pressure in the cylinder and therefore dependent on the surrounding temperature.
It is an object of the present invention to provide a biasing device in which the amount of extension or compression of the means providing the biasing force is less than the relative movement of the structures being biased.